1 /* 2 * watchdog_dev.c 3 * 4 * (c) Copyright 2008-2011 Alan Cox <alan@lxorguk.ukuu.org.uk>, 5 * All Rights Reserved. 6 * 7 * (c) Copyright 2008-2011 Wim Van Sebroeck <wim@iguana.be>. 8 * 9 * 10 * This source code is part of the generic code that can be used 11 * by all the watchdog timer drivers. 12 * 13 * This part of the generic code takes care of the following 14 * misc device: /dev/watchdog. 15 * 16 * Based on source code of the following authors: 17 * Matt Domsch <Matt_Domsch@dell.com>, 18 * Rob Radez <rob@osinvestor.com>, 19 * Rusty Lynch <rusty@linux.co.intel.com> 20 * Satyam Sharma <satyam@infradead.org> 21 * Randy Dunlap <randy.dunlap@oracle.com> 22 * 23 * This program is free software; you can redistribute it and/or 24 * modify it under the terms of the GNU General Public License 25 * as published by the Free Software Foundation; either version 26 * 2 of the License, or (at your option) any later version. 27 * 28 * Neither Alan Cox, CymruNet Ltd., Wim Van Sebroeck nor Iguana vzw. 29 * admit liability nor provide warranty for any of this software. 30 * This material is provided "AS-IS" and at no charge. 31 */ 32 33 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 34 35 #include <linux/module.h> /* For module stuff/... */ 36 #include <linux/types.h> /* For standard types (like size_t) */ 37 #include <linux/errno.h> /* For the -ENODEV/... values */ 38 #include <linux/kernel.h> /* For printk/panic/... */ 39 #include <linux/fs.h> /* For file operations */ 40 #include <linux/watchdog.h> /* For watchdog specific items */ 41 #include <linux/miscdevice.h> /* For handling misc devices */ 42 #include <linux/init.h> /* For __init/__exit/... */ 43 #include <linux/uaccess.h> /* For copy_to_user/put_user/... */ 44 45 #include "watchdog_dev.h" 46 47 /* make sure we only register one /dev/watchdog device */ 48 static unsigned long watchdog_dev_busy; 49 /* the watchdog device behind /dev/watchdog */ 50 static struct watchdog_device *wdd; 51 52 /* 53 * watchdog_ping: ping the watchdog. 54 * @wddev: the watchdog device to ping 55 * 56 * If the watchdog has no own ping operation then it needs to be 57 * restarted via the start operation. This wrapper function does 58 * exactly that. 59 * We only ping when the watchdog device is running. 60 */ 61 62 static int watchdog_ping(struct watchdog_device *wddev) 63 { 64 if (test_bit(WDOG_ACTIVE, &wddev->status)) { 65 if (wddev->ops->ping) 66 return wddev->ops->ping(wddev); /* ping the watchdog */ 67 else 68 return wddev->ops->start(wddev); /* restart watchdog */ 69 } 70 return 0; 71 } 72 73 /* 74 * watchdog_start: wrapper to start the watchdog. 75 * @wddev: the watchdog device to start 76 * 77 * Start the watchdog if it is not active and mark it active. 78 * This function returns zero on success or a negative errno code for 79 * failure. 80 */ 81 82 static int watchdog_start(struct watchdog_device *wddev) 83 { 84 int err; 85 86 if (!test_bit(WDOG_ACTIVE, &wddev->status)) { 87 err = wddev->ops->start(wddev); 88 if (err < 0) 89 return err; 90 91 set_bit(WDOG_ACTIVE, &wddev->status); 92 } 93 return 0; 94 } 95 96 /* 97 * watchdog_stop: wrapper to stop the watchdog. 98 * @wddev: the watchdog device to stop 99 * 100 * Stop the watchdog if it is still active and unmark it active. 101 * This function returns zero on success or a negative errno code for 102 * failure. 103 * If the 'nowayout' feature was set, the watchdog cannot be stopped. 104 */ 105 106 static int watchdog_stop(struct watchdog_device *wddev) 107 { 108 int err = -EBUSY; 109 110 if (test_bit(WDOG_NO_WAY_OUT, &wddev->status)) { 111 pr_info("%s: nowayout prevents watchdog to be stopped!\n", 112 wddev->info->identity); 113 return err; 114 } 115 116 if (test_bit(WDOG_ACTIVE, &wddev->status)) { 117 err = wddev->ops->stop(wddev); 118 if (err < 0) 119 return err; 120 121 clear_bit(WDOG_ACTIVE, &wddev->status); 122 } 123 return 0; 124 } 125 126 /* 127 * watchdog_write: writes to the watchdog. 128 * @file: file from VFS 129 * @data: user address of data 130 * @len: length of data 131 * @ppos: pointer to the file offset 132 * 133 * A write to a watchdog device is defined as a keepalive ping. 134 * Writing the magic 'V' sequence allows the next close to turn 135 * off the watchdog (if 'nowayout' is not set). 136 */ 137 138 static ssize_t watchdog_write(struct file *file, const char __user *data, 139 size_t len, loff_t *ppos) 140 { 141 size_t i; 142 char c; 143 144 if (len == 0) 145 return 0; 146 147 /* 148 * Note: just in case someone wrote the magic character 149 * five months ago... 150 */ 151 clear_bit(WDOG_ALLOW_RELEASE, &wdd->status); 152 153 /* scan to see whether or not we got the magic character */ 154 for (i = 0; i != len; i++) { 155 if (get_user(c, data + i)) 156 return -EFAULT; 157 if (c == 'V') 158 set_bit(WDOG_ALLOW_RELEASE, &wdd->status); 159 } 160 161 /* someone wrote to us, so we send the watchdog a keepalive ping */ 162 watchdog_ping(wdd); 163 164 return len; 165 } 166 167 /* 168 * watchdog_ioctl: handle the different ioctl's for the watchdog device. 169 * @file: file handle to the device 170 * @cmd: watchdog command 171 * @arg: argument pointer 172 * 173 * The watchdog API defines a common set of functions for all watchdogs 174 * according to their available features. 175 */ 176 177 static long watchdog_ioctl(struct file *file, unsigned int cmd, 178 unsigned long arg) 179 { 180 void __user *argp = (void __user *)arg; 181 int __user *p = argp; 182 unsigned int val; 183 int err; 184 185 if (wdd->ops->ioctl) { 186 err = wdd->ops->ioctl(wdd, cmd, arg); 187 if (err != -ENOIOCTLCMD) 188 return err; 189 } 190 191 switch (cmd) { 192 case WDIOC_GETSUPPORT: 193 return copy_to_user(argp, wdd->info, 194 sizeof(struct watchdog_info)) ? -EFAULT : 0; 195 case WDIOC_GETSTATUS: 196 val = wdd->ops->status ? wdd->ops->status(wdd) : 0; 197 return put_user(val, p); 198 case WDIOC_GETBOOTSTATUS: 199 return put_user(wdd->bootstatus, p); 200 case WDIOC_SETOPTIONS: 201 if (get_user(val, p)) 202 return -EFAULT; 203 if (val & WDIOS_DISABLECARD) { 204 err = watchdog_stop(wdd); 205 if (err < 0) 206 return err; 207 } 208 if (val & WDIOS_ENABLECARD) { 209 err = watchdog_start(wdd); 210 if (err < 0) 211 return err; 212 } 213 return 0; 214 case WDIOC_KEEPALIVE: 215 if (!(wdd->info->options & WDIOF_KEEPALIVEPING)) 216 return -EOPNOTSUPP; 217 watchdog_ping(wdd); 218 return 0; 219 case WDIOC_SETTIMEOUT: 220 if ((wdd->ops->set_timeout == NULL) || 221 !(wdd->info->options & WDIOF_SETTIMEOUT)) 222 return -EOPNOTSUPP; 223 if (get_user(val, p)) 224 return -EFAULT; 225 if ((wdd->max_timeout != 0) && 226 (val < wdd->min_timeout || val > wdd->max_timeout)) 227 return -EINVAL; 228 err = wdd->ops->set_timeout(wdd, val); 229 if (err < 0) 230 return err; 231 /* If the watchdog is active then we send a keepalive ping 232 * to make sure that the watchdog keep's running (and if 233 * possible that it takes the new timeout) */ 234 watchdog_ping(wdd); 235 /* Fall */ 236 case WDIOC_GETTIMEOUT: 237 /* timeout == 0 means that we don't know the timeout */ 238 if (wdd->timeout == 0) 239 return -EOPNOTSUPP; 240 return put_user(wdd->timeout, p); 241 case WDIOC_GETTIMELEFT: 242 if (!wdd->ops->get_timeleft) 243 return -EOPNOTSUPP; 244 245 return put_user(wdd->ops->get_timeleft(wdd), p); 246 default: 247 return -ENOTTY; 248 } 249 } 250 251 /* 252 * watchdog_open: open the /dev/watchdog device. 253 * @inode: inode of device 254 * @file: file handle to device 255 * 256 * When the /dev/watchdog device gets opened, we start the watchdog. 257 * Watch out: the /dev/watchdog device is single open, so we make sure 258 * it can only be opened once. 259 */ 260 261 static int watchdog_open(struct inode *inode, struct file *file) 262 { 263 int err = -EBUSY; 264 265 /* the watchdog is single open! */ 266 if (test_and_set_bit(WDOG_DEV_OPEN, &wdd->status)) 267 return -EBUSY; 268 269 /* 270 * If the /dev/watchdog device is open, we don't want the module 271 * to be unloaded. 272 */ 273 if (!try_module_get(wdd->ops->owner)) 274 goto out; 275 276 err = watchdog_start(wdd); 277 if (err < 0) 278 goto out_mod; 279 280 /* dev/watchdog is a virtual (and thus non-seekable) filesystem */ 281 return nonseekable_open(inode, file); 282 283 out_mod: 284 module_put(wdd->ops->owner); 285 out: 286 clear_bit(WDOG_DEV_OPEN, &wdd->status); 287 return err; 288 } 289 290 /* 291 * watchdog_release: release the /dev/watchdog device. 292 * @inode: inode of device 293 * @file: file handle to device 294 * 295 * This is the code for when /dev/watchdog gets closed. We will only 296 * stop the watchdog when we have received the magic char (and nowayout 297 * was not set), else the watchdog will keep running. 298 */ 299 300 static int watchdog_release(struct inode *inode, struct file *file) 301 { 302 int err = -EBUSY; 303 304 /* 305 * We only stop the watchdog if we received the magic character 306 * or if WDIOF_MAGICCLOSE is not set. If nowayout was set then 307 * watchdog_stop will fail. 308 */ 309 if (test_and_clear_bit(WDOG_ALLOW_RELEASE, &wdd->status) || 310 !(wdd->info->options & WDIOF_MAGICCLOSE)) 311 err = watchdog_stop(wdd); 312 313 /* If the watchdog was not stopped, send a keepalive ping */ 314 if (err < 0) { 315 pr_crit("%s: watchdog did not stop!\n", wdd->info->identity); 316 watchdog_ping(wdd); 317 } 318 319 /* Allow the owner module to be unloaded again */ 320 module_put(wdd->ops->owner); 321 322 /* make sure that /dev/watchdog can be re-opened */ 323 clear_bit(WDOG_DEV_OPEN, &wdd->status); 324 325 return 0; 326 } 327 328 static const struct file_operations watchdog_fops = { 329 .owner = THIS_MODULE, 330 .write = watchdog_write, 331 .unlocked_ioctl = watchdog_ioctl, 332 .open = watchdog_open, 333 .release = watchdog_release, 334 }; 335 336 static struct miscdevice watchdog_miscdev = { 337 .minor = WATCHDOG_MINOR, 338 .name = "watchdog", 339 .fops = &watchdog_fops, 340 }; 341 342 /* 343 * watchdog_dev_register: 344 * @watchdog: watchdog device 345 * 346 * Register a watchdog device as /dev/watchdog. /dev/watchdog 347 * is actually a miscdevice and thus we set it up like that. 348 */ 349 350 int watchdog_dev_register(struct watchdog_device *watchdog) 351 { 352 int err; 353 354 /* Only one device can register for /dev/watchdog */ 355 if (test_and_set_bit(0, &watchdog_dev_busy)) { 356 pr_err("only one watchdog can use /dev/watchdog\n"); 357 return -EBUSY; 358 } 359 360 wdd = watchdog; 361 362 err = misc_register(&watchdog_miscdev); 363 if (err != 0) { 364 pr_err("%s: cannot register miscdev on minor=%d (err=%d)\n", 365 watchdog->info->identity, WATCHDOG_MINOR, err); 366 goto out; 367 } 368 369 return 0; 370 371 out: 372 wdd = NULL; 373 clear_bit(0, &watchdog_dev_busy); 374 return err; 375 } 376 377 /* 378 * watchdog_dev_unregister: 379 * @watchdog: watchdog device 380 * 381 * Deregister the /dev/watchdog device. 382 */ 383 384 int watchdog_dev_unregister(struct watchdog_device *watchdog) 385 { 386 /* Check that a watchdog device was registered in the past */ 387 if (!test_bit(0, &watchdog_dev_busy) || !wdd) 388 return -ENODEV; 389 390 /* We can only unregister the watchdog device that was registered */ 391 if (watchdog != wdd) { 392 pr_err("%s: watchdog was not registered as /dev/watchdog\n", 393 watchdog->info->identity); 394 return -ENODEV; 395 } 396 397 misc_deregister(&watchdog_miscdev); 398 wdd = NULL; 399 clear_bit(0, &watchdog_dev_busy); 400 return 0; 401 } 402